1. Field of the Invention
The present invention relates to a forced-induction system for an internal combustion engine. More particularly, the present invention relates to a turbocharger system for increasing the power and efficiency of an internal combustion engine run at low speed and heavy load.
2. Description of the Related Art
A turbocharger used as means for providing forced induction to increase power and improve fuel efficiency of an internal combustion engine, particularly an automobile engine, employs exhaust energy to rotate an exhaust turbine connected by a shaft to an intake compressor. The compressor compresses the air-fuel mixture or intake air that is subsequently mixed with fuel to increase the energy obtained from the ignition of the air-fuel mixture in the cylinders.
The improvements achievable by turbocharging an internal combustion engine, however, are influenced by the running conditions of the vehicle. In general, satisfactory forced induction from a turbocharger can be expected if the pressure and temperature of the exhaust gas driving the turbine are above certain levels. Exhaust gas temperature is a particularly important factor in achieving high-speed rotation of the turbine when the vehicle is run at a moderate or high speed and under a heavy load. In contrast, a turbocharger often makes no specific contribution to improvement of the output of the engine when the engine is run at a low speed and under a heavy load. Low-speed, high-load conditions in a turbocharged engine produce a decrease in both the pressure of exhaust gas generated and in the exhaust gas temperature when compared to moderate or high speed conditions. It is generally believed that the higher the exhaust gas temperature, the better the turbine efficiency.
Although attempts have been made to increase exhaust gas temperature by providing an ignition time lag or by increasing intake air temperature, such methods have inherent disadvantages. The former involves a trade off in fuel combustion efficiency and stability, and the latter produces a reduction in the volume of oxygen inducted into the cylinders or in the durability of the engine because of the resulting temperature and pressure increase in the cylinders.
It is an object of the present invention to provide an improved internal combustion engine with a turbocharger that is capable of performing a forced induction function satisfactorily at low engine speed and high load without lowering fuel combustion efficiency or durability of the engine.
Additional objects and advantages of the present invention will be set forth in part in the description that follows and in part will be obvious from that description or can be learned by practice of the invention. The objects and advantages of the invention can be realized and obtained by the system particularly pointed out in the appended claims.